Respiratory System PDF

Anatomy physiology Chapter 1 : The respiratory system Dr Hanane Yassine  Overview  All organs use oxygen (O2) and reject carbon dioxide (CO2) permanently  These gas exchanges increases when our organs are active  The function of the respiratory system is to brin...

Anatomy physiology Chapter 1 : The respiratory system Dr Hanane Yassine  Overview  All organs use oxygen (O2) and reject carbon dioxide (CO2) permanently  These gas exchanges increases when our organs are active  The function of the respiratory system is to bring atmospheric oxygen to the blood which distributes it throughout the body and to reject carbon dioxide The organs of the respiratory system The nose The pharynx The larynx The trachea The 2 bronchi The bronchioles The two lungs, and the pleura that covers them Muscles of breathing – the intercostal muscles and the diaphragm  Nose and nasal cavity The nasal cavity is the main route of air entry Large irregular cavity divided into two equal passages by a septum The posterior part (bony) of the septum is formed by the perpendicular plate of the ethmoid bone and the vomer The Anterior part of the septum consists of hyaline cartilage The roof is formed by the cribriform plate of the ethmoid bone , the sphenoid bone, frontal bone and nasal bones The floor is formed by the roof of the mouth and consists of the hard palate in front (composed of the maxilla and palatine bones) and the soft palate behind (consists of involuntary muscle)  Lining of the nasal cavity The nasal cavity is lined with ciliated columnar epithelium Highly vascularized and contains mucus-secreting goblet cells The epithelium blends at the anterior nares with the skin and posteriorly it extends into the nasal part of the pharynx (the nasopharynx)  Openings into the nasal cavity The anterior nares, or nostrils : are the openings from the exterior into the nasal cavity. Nasal hairs are found here, coated in sticky mucus The posterior nares : are the openings from the nasal cavity into the pharynx The paranasal sinuses : are cavities in the bones of the face and the cranium, containing air. There are tiny openings between the paranasal sinuses and the nasal cavity. The main sinuses are: - Maxillary sinuses - Frontal and sphenoidal sinuses - Ethmoidal sinuses  The sinuses are involved in speech and also lighten the skull. The nasolacrimal ducts extend from the lateral walls of the nose to the conjunctival sacs of the eye. They drain tears from the eyes  Functions of the nose In the nasal cavity, air is warmed, moistened and filtered  this is facilitated by the three three conchae The three conchae increase the surface area and cause turbulence, spreading inspired air over the whole nasal surface The large surface area maximizes warming, humidification and filtering  Functions of the nose Warming : The immense vascularity of the mucosa permits rapid warming as the air flows Humidification : As air travels over the moist mucosa, it becomes saturated with water vapour Filtering and cleaning : Hairs at the anterior nares trap larger particles. Smaller particles such as dust and bacteria settle and adhere to the mucus. Beating of the cilia wafts the mucus towards the throat where it is swallowed or expectorated Olfaction : Specialized receptors that detect smell are located in the roof of the nose in the area of the cribriform plate of the ethmoid bones and the superior conchae. These receptors are stimulated by airborne odours. The nerve signals are carried by the olfactory nerves to the brain where the sensation of smell is perceived  The pharynx The pharynx (throat) is a passageway about 12–14 cm long It extends from the posterior nares, and runs behind the mouth and the larynx to the level of the 6th thoracic vertebra, where it becomes the oesophagus The pharynx is divided into three regions - Nasopharynx: superior; communicates with nasal cavities - Oropharynx: middle, behind the oral cavity, and communicates with the laryngopharynx - Laryngopharynx: inferior, connects with the larynx and narrows in the form of a funnel towards the esophagus  The nasopharynx The pharynx lies behind the nose above the level of the soft palate On its lateral walls are the two openings of the auditory tubes On the posterior wall are the pharyngeal tonsils (adenoids)  The oropharynx The oral part of the pharynx lies behind the mouth Extending from below the level of the soft palate to the level of the upper part of the body of the 3rd cervical vertebra The lateral walls of the pharynx blend with the soft palate to form two folds on each side Between each pair of folds is a collection of lymphoid tissue called the palatine tonsil When swallowing, the soft palate and uvula are pushed upwards sealing off the nasal cavity and preventing the entry of food and fluids  The laryngopharynx The laryngeal part of the pharynx extends from the oropharynx above and continues as the oesophagus below, with the larynx lying anteriorly  Structure of the pharynx The walls of the pharynx contain several types of tissue.  Mucous membrane lining Varies slightly in the different regions In the nasopharynx : consists of ciliated columnar epithelium; In the oropharynx and laryngopharynx : it is formed by stratified squamous epithelium This lining protects underlying tissues from the abrasive action of foodstuffs passing through during swallowing  Submucosa It is the layer of tissue below the epithelium Rich in mucosa-associated lymphoid tissue (MALT), involved in protection against infection Tonsils are masses of MALT that bulge through the epithelium. Some glandular tissue is also found in submucosa  Structure of pharynx  Smooth muscle The pharyngeal muscles help to keep the pharynx permanently open so that breathing is not interfered with Sometimes in sleep, the use of sedative drugs or alcohol may the reduce these muscles tone  the opening through the pharynx can become partially or totally obstructed This contributes to snoring and periodic wakenings, which disturb sleep. Constrictor muscles close the pharynx during swallowing, pushing food and fluid into the oesophagus  Fonctions of the pharynx  Passageway for air and food : air passes through the nasal and oral sections, and food through the oral and laryngeal sections  Warming and humidifying : By the same methods as in the nose, the air is further warmed and moistened as it passes towards the lungs  Deglutition: transit of ingested food from the mouth to the esophagus  Hearing : The auditory tube, extending from the nasopharynx to each middle ear, allows air to enter the middle ear  equal pressure between the middle and outer ear, which protects the tympanic membrane from any change in atmospheric pressure  Fonctions of the pharynx  Speech : The emission of vocal sound is due to the vibration of the vocal cords, located in the larynx. The pharynx plays a role of amplification and resonance (it contributes to give the voice its individual characteristics)  Protection : The lymphatic tissue of the pharyngeal and laryngeal tonsils produces antibodies in response to swallowed o inhaled  3. The larynx The larynx or voice box links the laryngopharynx and the trachea It lies in front of the laryngopharynx and the 3rd, 4th, 5th and 6th cervical vertebrae Musculocartilaginous structure  Structures associated with the larynx - Superiorly : the hyoid bone and the root of the tongue - Inferiorly : it is continuous with the trachea - Anteriorly : the muscles attached to the hyoid bone and the muscles of the neck - Posteriorly : the laryngopharynx - Laterally : the lobes of the thyroid gland  Structure of the larynx  Cartilages The larynx is composed of several irregularly shaped cartilages attached to each other by ligaments and membranes. The main cartilages are : - 1 thyroïd cartilage - 1cricoïd cartilage - 2 arytenoïd cartilages - 1 epiglottis  Stucture of larynx  The thyroïd cartilage : The most prominent of the laryngeal cartilages, it forms most of the anterior and lateral walls of the larynx Made of hyaline cartilage Its anterior wall form the laryngeal prominence or Adam’s apple. It is partially divided by the thyroid notch The cartilage is incomplete posteriorly It is bound with ligaments to the hyoid bone above and the cricoid cartilage below  Structure of larynx  The cricoïd cartilage: This lies below the thyroid cartilage and is composed of hyaline cartilage. It is shaped like a signet ring, completely encircling the larynx with the narrow part anteriorly and the broad part posteriorly The broad posterior part articulates with the arytenoid cartilages and with the thyroid cartilage The lower border of the cricoid cartilage marks the end of the upper respiratory tract.  Structure of larynx  Arytenoïd cartilages : Two pyramidal hyaline cartilages, located at the top of the large part of the cricoid cartilage (posterior) The vocal cords, as well as muscles, are attached to it  Structure of larynx  The epiglottis : Fibroelastic cartilage attached to the inner surface of the anterior wall of the thyroid cartilage immediately below the thyroid notch It rises obliquely upwards behind the tongue and the body of the hyoid bone During swallowing the epiglottis closes the larynx protecting the lungs from accidental inhalation of a foreign body  Interior of the larynx : The vocal cords The vocal cords are two pale folds of mucous membrane stretched across the laryngeal opening They extend from the inner wall of the thyroid prominence (anteriorly) to the arytenoid cartilages (posteriorly) Each cord is made of the thyroarytenoid muscle and the elastic vocal ligament at the inner edge of the cord The space between the vocal cords is called the glottis  Interior of the larynx : The vocal cords Abducted vocal cords (open) : When the muscles controlling the vocal cords are relaxed  the vocal cords open and the passageway for air coming up through the larynx is clear  vocal cord vibrations produces low-pitched sounds Adducted vocal cords (closed): When the muscles controlling the vocal cords contract the vocal cords are stretched out tightly and are closed. When the vocal cords are vibrated by air passing through from the lungs, the sound produced is high pitched.  Fonctions of larynx  Production of sound: Sound has the properties of pitch, volume and resonance Pitch of the voice : depends upon the length and tightness of the cords. (short cords  higher pitched sounds, long cords  low-pitched sounds) Volume of the voice : depends upon the force with which the cords vibrate. The greater the force of expired air, the more strongly the cords vibrate and the louder the sound emitted Resonance (tone) : dependent upon the shape of the mouth, the position of the tongue and the lips, the facial muscles and the air in the paranasal sinuses  Fonctions of larynx Protection of the lower respiratory tract : During swallowing, the epiglottis closes the larynx. This allows the food to pass into the esophagus and not into the trachea Passageway for air : The larynx links the pharynx above with the trachea below. Humidifying, filtering and warming : These processes continue as inspired air travels through the larynx  4. The trachea The trachea, follows the larynx with a length of about 10 to 11 cm It lies in front of the oesophagus It extends downwards to about the level of the 5th thoracic vertebra where it divides at the carina into the right and left primary bronchi, one bronchus going to each lung  Structures associated with the trachea Superiorly : the larynx Inferiorly : the right and left bronchi Anteriorly : upper part: the isthmus of the thyroid gland lower part: the arch of the aorta and the sternum Posteriorly : the oesophagus Laterally : the lungs and the lobes of the thyroid gland  Structure of the trachea Flexible air duct Composed of 16 to 20 incomplete (C-shaped) rings of hyaline cartilage lying one above the other The rings are incomplete posteriorly where the trachea lies against the oesophagus The cartilages are embedded in a sleeve of smooth muscle and connective tissue, which forms the posterior wall The lining is ciliated containing mucus-secreting goblet cells. This mucous membrane retains dust and debris and carries them up the throat to be swallowed or expectorated.  Fonctions of the trachea  Support and patency: - Tracheal cartilages hold the trachea permanently open (patent), the soft tissue bands in between the cartilages allow flexibility so that the head and neck can move freely without obstructing or kinking the trachea - The absence of cartilage posteriorly permits the oesophagus to expand comfortably during swallowing. - Contraction or relaxation of the trachealis muscle helps to regulate the diameter of the trachea  Mucociliary escalator : The regular and synchronized beating of the cilia of the mucous membrane propels mucus and foreign particles to the larynx, where they are swallowed or expectorated  Fonctions de la trachée  Warming, humidifying and filtering  Cough reflex: Nerve endings in the larynx, trachea and bronchi are sensitive to irritation. The reflex motor response by deep inspiration followed by closure of the glottis (closure of the vocal cords). The abdominal and respiratory muscles then contract causing a sudden and rapid increase of pressure in the lungs  glottis opens, expelling air through the mouth, taking mucus and/or foreign material with it.  5. The lungs  The lungs are 2 spongy masses, located in the thorax on both sides of the heart  Right Lung is divided into 3 lobes separated by 2 fissures  Left lung is divided into 2 lobes separated by 1 fissure  Limited by the ribs and closed below  Each lobe is made up of a large by a muscle: the diaphragm number of lobules  The lungs They are cone-shaped and have an: - Apex - Base - Costal surface : the broad outer surface of lung - Medial surface :The medial surface of each lung faces the other directly across the space between the lungs, the mediastinum. Each medial surface has a triangular- shaped area, called the hilum The mediastinum: the space between the 2 lungs. It contains the heart, the trachea, the large vessels, the main bronchi and the nerves...  The Lungs  Surrounded by a serosa = the pleura  The pleura consists of 2 layers: Parietal: enveloping the inner wall of thorax and the thoracic surface of the diaphragm  Visceral: enveloping the lung  Spaces Between the 2 layers correspond to the pleural cavity lubricated with pleural fluid  Pleural cavity Contains no air, so the pressure within is negative relative to atmospheric pressure Pleural fluid, allows the two layers of pleura to glide over each other, preventing friction between them during breathing There is superficial tension between the layers of pleura and the pleural fluid  It is essential for the lung to remain inflated If either layer of pleura is punctured, air is sucked into the pleural space and the entire lung collapses Pleural space participates in the defense of the lungs against inflammation and infections  Interior of the lungs The lungs are composed of the bronchi and bronchioles , alveoli, connective tissue, blood vessels, lymph vessels and nerves, all embedded in an elastic connective tissue matrix Each lobe is made up of a large number of lobules  Bronchi The two primary bronchi are formed when the trachea divides : the right bronchus and the left bronchus The right bronchus : - This is wider, shorter and more vertical than the left bronchus - After entering the right lung at the hilum it divides into three branches, one to each lobe - Each branch then subdivides into progressively smaller airways The left bronchus : - After entering the lung at the hilum it divides into two branches, one to each lobe - Each branch then subdivides into progressively smaller airways within the lung  Each main bronchus (L/R) divides by decreasing in caliber: - Lobar bronchus (3 on the right and 2 on the left) - Segmental bronchus - Bronchioles  Successive divisions lead to terminal bronchioles, respiratory bronchioles, and alveolar ducts and alveoli  Structural changes in the bronchial passages As the bronchi divide and become progressively smaller, their structure changes to match their function.: - The cartilage: present for support in the larger airways (trachea, primary bronchi). At the bronchiolar level there is no cartilage present in the airway walls at all - Smooth muscle: As the cartilage disappears from airway walls, it is replaced by smooth muscle. This allows the diameter of the airways to be increased or decreased through the influence of the autonomic nervous system, regulating airflow within each lung - Epithelium: The ciliated epithelium is gradually replaced with non- ciliated epithelium, and goblet cells disappear  Bronchial contractility  Ability of bronchi to change their diameter by the contraction or relaxation of the smooth muscles of their wall  Regulates the speed and the volume of airflow into and within the lungs  Smooth muscles are under the control of the autonomic nervous system: - Parasympathetic: bronchoconstrictor - Sympathetic: bronchodilator  Bronchial contractility Parasympathetic system Sympathetic system acetylcholine Adrenaline 1 2 Bronchial smooth muscle Bronchoconstriction Bronchodilation  The alveoli Within each lobe, the lung tissue is further divided by fine sheets of connective tissue into lobules Each lobule is supplied with air by a terminal bronchiole, which further subdivides into respiratory bronchioles, alveolar ducts and large numbers of alveoli (air sacs) There are about 150 million alveoli in the adult lung  The alveoli The alveolar wall is composed of a single layer of squamous epithelial cells The alveoli are surrounded by a dense network of very thin and semi- permeable capillaries allowing gas exchange Exchange of gases in the lung (external respiration) takes place across a membrane made up of the alveolar wall and the capillary wall fused firmly together. This is called the respiratory membrane Lying between the squamous cells are septal cells that secrete surfactant, a phospholipid fluid which prevents the alveoli from drying out and reduces surface tension preventing alveolar collapse during expiration  The respiration Respiration in steps : Pulmonary ventilation External respiration Internal respiration  Pulmonary ventilation  Process with 3 phases : - air enters the lungs = inspiration - Air exit the lungs = expiration - Pause  The average breathing rate is 12 to 15 breaths per minute  Respiratory muscles Expansion of the chest during inspiration occurs as a result of muscular activity, partly voluntary and partly involuntary The main muscles used in normal breathing are the external intercostal muscles and the diaphragm  The external intercostal muscles : They are involved in inspiration The first rib is fixed  when the external intercostal muscles contract they pull all the other ribs towards the first rib  The ribcage moves as a unit, upwards and outwards, enlarging the thoracic cavity  Respiratory muscles  Diaphragm: The diaphragm is a dome-shaped muscular structure separating the thoracic and abdominal cavities consists of a central tendon from which muscle fibres radiate to be attached to the lower ribs and sternum and to the vertebral column During contraction, muscle fibres shorten and the central tendon is pulled downwards: - lengthening the thoracic cavity  decreasing pressure in the thoracic cavity - Lowering of the abdominal viscera  increasing the pressure in the abdominal and pelvic cavities  Pulmonary ventilation : Inspiration Mechanism : - Contraction of the external intercostal muscles and the diaphragm  dilation of the thorax - The parietal pleura that adheres to the diaphragm and the inside of the rib cage is also pulled outwards  This also pulls the visceral pleura outwards - The latter adhering firmly to the lung will result in the dilation of the lungs  the pressure in the alveoli as well as in the air ducts will decrease - This draws air into the lungs in an attempt to equalize atmospheric and alveolar air pressure  Pulmonary respiration : inspiration intrapulmonary P < atm P : the air enters the lungs The process of inspiration is active, as it requires energy for muscle contraction. At rest, an inspiration lasts about 2 seconds.  Pulmonary ventilation: expiration Mechanism : - Relaxation of the external intercostal muscles and the diaphragm leads to a reduction in thoracic volume and an elastic return of the lungs - When this happens, the pressure in the lungs increases, and air is expelled from the airways. - At the end of exhalation, the lung still contains a certain amount of air, and an intact pleura prevents it from collapsing completely - Expiration is passive, as it does not require energy Pulmonary ventilation: expiration Intrapulmonary P>atmP : air exit the lungs  Physiological variables affecting breathing Elasticity : is the ability of the lung to return to its normal shape after each breath. Loss of elasticity, necessitates forced expiration and increased effort on inspiration Compliance : is the stretchability of the lungs. This is the effort required to inflate the alveoli. When compliance is low the effort needed to inflate the lungs is greater than normal Airway resistance : When this is increased, e.g. in bronchoconstriction, more respiratory effort is required to inflate the lungs  Lung volumes and capacities Tidal volume (TV) : This is the amount of air passing into and out of the lungs during each cycle of breathing (500 mL at rest) Inspiratory reserve volume (IRV) : This is the extra volume of air that can be inhaled into the lungs during maximal inspiration, i.e. over and above normal TV (1,9 litre chez la femme, 2,4 litres chez l'homme)  Lung volumes and capacities Inspiratory capacity (IC): This is the amount of air that can be inspired with maximum effort. It consists of the tidal volume (500 ml) plus the inspiratory reserve volume. CI = IRV+ TV Fuctional residual capacity (FRC): This is the amount of air remaining in the air passages and alveoli at the end of quiet expiration Expiratory reserve volume (ERV) : This is the largest volume of air which can be expelled from the lungs during maximal expiration  Lung volumes and capacities Residual volume (RV): is the volume of air remaining in the lungs after forced expiration Vital capacity (VC) : is the maximum volume of air which can be moved into and out of the lungs: VC= IC + ERV = IRV + TV + ERV Total lung capacity (TLC): This is the maximum amount of air the lungs can hold. In an adult of average build, it is normally around 6 litres. Total lung capacity represents TLC=VC+RV  External respiration  Gas exchange by diffusion between the pulmonary alveoli and the blood of the alveolar capillaries through the respiratory membrane  During this process, the blood : - Becomes enriched in O2 - Rejects CO2 Heart and lungs are related External respiration Exchanges at the level of the alveoli  Internal respiration Gas exchange between the blood of the systemic capillaries and the cells of the tissues The blood loses O2 and is enriched in CO2 Internal respiration  Transport of gases in the bloodstream Oxygen and carbon dioxide are transported in the blood in different ways.  Oxygen transport - 98.5 % bound to hemoglobin (oxyhemoglobin) - 1.5 % dissolved in plasma Oxyhemoglobin is unstable and dissociates easily by releasing oxygen Factors that increase dissociation include low O2 levels, low pH and increased body temperature In active tissues, CO2 and heat production is increased  releases of oxygen at this level  Transport of gases in the bloodstream Transport of carbon dioxide - 70% in the form of bicarbonate ion (HCO3-) - 23% bound to hemoglobin (carboxyhemoglobin) - 7% dissolved in plasma